DB Level Locking (https://jira.mongodb.org/browse/SERVER-4328) is a dependency of Collection Level Locking (https://jira.mongodb.org/browse/SERVER-1240). For a critical, tricky core piece of functionality like this it makes sense to tackle one major concurrency issue at a time, do a release, stabilise the code and verify there are no issues introduced by the new locking code and only then release the next step in locking enhancements. Doesn't seem like they're "pretending" about anything as far as I can tell.